THE INFLUENCE OF MINERAL ADMIXTURES AND POLYPROPYLENE FIBERS ON DENSITY AND ULTRASONIC PULSE VELOCITY OF SELF-COMPACTING FIBER-REINFORCED CONCRETE

DR.Ghazwan AbdulSamad Salman Ministry of Higher Education And Scientific Research, Reconstruction And Projects Directorate, Bagdad/Iraq *

ABSTRACT : The effect of metakaoline , silica fume and polypropylene fibers on density and ultrasonic pulse velocity of self compacting concrete and self compacting fiber-reinforced concrete were investigated and compared in this study. Fifteen SCC mixes were prepared with two types of mineral admixtures and polypropylene fibers. Metakaoline and silica fume were used as mineral admixtures, while polypropylene fibers were used as fiber inclusions. Two different fiber lengths (6mm and 12mm) and fiber volume (0,1 % and 0,5 %) were used. Different parameters such as slump flow diameter, T500time, V-funnel time, blocking ratio and filling height difference were assessed to evaluate fresh state properties. The main objective of this study is to investigate the behaviors of ultrasonic pulse velocity through mineral admixtures and polypropylene fiber reinforced self-compacted concrete with respect to volume fraction and lengths of polypropylene fibers, curing periods . Tables were prepared to evaluate the ultrasonic pulse velocity for all SCCFRC mixes cured in water for 7, 28, 90 and 180 days. It was found that, the addition of polypropylene fibers in self-compacted concrete can decreases the ultrasonic pulse velocity. Keywords; SCC, fibers, mineral admixture, ultrasonic pulse velocity.

1 INTRODUCTION Self compacting concrete (SCC) can be defined as that exhibiting substantial flow ability to fill the formwork through congested reinforcement or any other obstacle under no other force than gravitation while processing enough viscosity to be stable against segregation thereby remain homogenous through transportation, pumping, and placing into formwork. The addition of small amount of non-metallic fibers such as glass, polyester, polypropylene etc, results in good SCC properties such as increasing ductility, mechanical performance (Pons et al,2007), frost resistance (Persson et al,2006)), preventing fire spalling (Liu et al,2007)) and improved durability (Bauml et al,2001)). The ultrasonic test is a useful tool for assessing the uniformity of concrete and detecting cracks and voids. It gives useful information about size of micro-cracks zone, crack growth and the interior structure of the concrete element. Ultrasonic pulse velocity (UPV) non-destructive test method was employed in this study to assess the polypropylene FRSCC. Even though, the application of UPV for materials characterization started three decades ago (Belayhun 2013), its behaviors through polypropylene FRSCC have not been identified yet. (Panzera et al 2008) discovered a linear correlation between UPV and bulk density represented by the equation

y = 1506.9x + 541.7 (R2= 88.69%), where y is the pulse velocity and x the bulk density. Many researchers tried to suggest the common limits for the UPV to different qualities of concrete .Concretes are classified as excellent, good, doubtful, poor, and very poor for (4.8km/s)and above , (3.66–4.57km/s) , (3.50–3.66km/s) , (2.14–3.0km/s) and (2.14km/s) and below UPV values, respectively (Jones et al (2007)) .The main objective of this study is to investigate the behaviors of UPV through polypropylene FRSCC with respect to fiber length (6mm and 12mm) , fiber fraction (0,1 % and 0,5 %), types of mineral admixtures for curing periods (7 days, 28 days, and 90 days). The research was a part of continuous study which was done by (Salman (2013)) about the effect of Mineral admixtures and fibers on properties of SCC.

2 MATERIALS , MIX DESIGN AND APPLIED TESTS 2.1.1 Cement

Ordinary Portland cement (OPC) type (I) manufactured in Turkey was used. Tables (1) and (2) show the percentage oxide composition and physical properties of the cement used respectively, which corresponds to ASTM Type I cement. The cement content of all mixtures were kept constant at 500kg/m3 throughout this study. 2.1.2 Aggregate

natural sand and gravel were used as fine and coarse aggregate in this study. Table (3) shows the grading of sand and gravel. the coarse and fine aggregate had a specific gravity of 2.68 and 2.65 kg/m3, water absorptions of 0.6% and 2.2%, and sulfate content of 0.08 and 0.05, respectively. 2.1.3 Chemical admixture

A copolymer based superplasticiser Glenium 51, which was made for the production of high performance concrete is used. Its relative density was 1.1 g/cm3 @ 20 °C and a PH value of 6.6. 2.1.4 Mineral admixtures

High reactive Metakaoline (HRM) was used in this study. This HRM is an alumina silicate pozzolan produced by clinking the kaolin at temperatures of 700°C. Locally available kaolin clinks in laboratory using a fixed bed furnace for one hour duration at 700°C and then left to cool down. Metakaoline had a specific gravity of 2.62 kg/m3 and surface area of 19000cm2/g. Silica fume used is (Elkem micro SF) produced by Efaco company in Egypt. Silica fume had a specific gravity of 2.45 kg/m3.The chemical properties of the HRM and SF used are given in Table (1). 2.1.5 Fibers

The polypropylene fibers had a specific gravity of 0.91 kg/m3,Young modulus of 5.5 (GPA), Tensile strength of 350(MPA), Elongation at break of15%, Design thickness of 0.04 mm, Aspect ratio of 150 to 300 and with two different lengths were used in this study(6-12)mm.

2.2 Mix proportions, Mixing and curing

A total of fifteen mixes were prepared with different cementations materials constitutions. It was expected that fibers affect deformability and flow ability of reference mixes. For this reason mixes were proportioned at the upper level of self compacting ability in order to remain within the given limits (The European Guidelines, 2005) after the addition of fibers. Mix no. 1 , 2 and 3 represents SCC reference mixes and Mix no. 4 through 15 represent SCC mixes produced by using polypropylene fibers . Notation used for the mixes is as follows. For all mixes SCC represent self-compacting concrete while M and S denoted to the SCC with Metakaolin and silica

fume, respectively. The numbers 0.1 or 0.5 represent the volume fraction of fiber (0,1 % and 0,5 % respectively), letters P show the polypropylene fiber used and the last number represents the length of fiber used. As an example, SCC0.5P12 shows the SCC mix made without mineral admixtures, by using 0,5 % of 12 mm long polypropylene fibers. For reference mixes a single concrete mix of (1:2.08:0.96) (cement: fine aggregate: coarse aggregate) in proportion by weight and (0.35) water/cement are used. The same mix is used for the SCCS and SCCM except superplasticiser and SF or HRM were added. The Silica fume in some mixes was added by 10% of weight of cement while HRM were added in others with the same ratio. w/cement or w/binder ratio were kept constant at (0.35) for all SCC mixes. All cement dosages were kept constant at 500kg/m3 for all mixes. For all SCC mixes containing mineral admixtures, super plasticizer dosage was increased properly to maintain self compacting ability within the given limits (The European Guidelines, 2005) . The super plasticizer dosage for all SCC mix made without mineral admixtures was 8% by weight of cement while the dosage of all SCC mixes containing SF, become 9% and all SCC mixes containing HRM become 10% by weight of cement . The ingredients were mixed in an electrical pan mixer which has a capacity of 0,1 m. The mixing procedure which developed by(Walraven and Grunewald,2001 )was adopted. The procedure used was as follows; first binding materials and sand were dry mixed for 10 seconds, then water and superplasticizer added and materials were mixed for 110 seconds, after gravel was added and mixture was blended for 60 s, and finally fibers were put and the mix stirred for 90s. Then, materials were cast into steel moulds. After casting, specimens were placed immediately in moist cabinet maintained at a temperature of 23 ±2 and a relative humidity of about 95% for 24 hours. After that specimens were demolded and stored in tap water until the time of test.

Table (1) Chemical Properties of Portland Cement Table (2) Physical properties of cement.

Table (3) Grading of fine and coarse aggregates

Physical properties Test result

Specific surface area(Blaine method),m2/kg

2850

Setting time (Vicat’s method)

Initial setting time (min )

Final setting time (min )

130

205

Compressive strength (MPa)

3 days

7 days

17.37

26.66

Soundness: Autoclave % 0.34

Component (%) Ct SF MK

SiO2 19.9 94 51.3

CaO 60.8 Nil 3.00

MgO 1.5 2.00 0.17

Fe2O3 3.0 1.32 2.3

Al2O3 5.69 2.03 33.4

SO3 2.3 -------- 0.15

L.O.I 1.5 -------- 7.8

I.R 1.1 -------- -----

L.S.F 0.85 -------- -----

C3S 47.1

-------- -----

C2S 21.5

-------- -----

C3A 10 -------- -----

C4AF 9.12 -------- -----

Pozzolanic activity 158.8 164.

Sieve % passing Sieve % passing

14 100 1.18 82.56

10 89 0.6 64.81

4.75 100 14 0.3 20.9

2.36 89.3 2.3 0.15 3.22

2.3 Applied tests 2.3.1 Fresh state tests

Fresh state properties of SCC mixes were evaluated by using some of the most commonly used methods (The European Guidelines, 2005) .The methods used were slump flow, V-funnel, L-box and U-box. 2.3.2 Hardened State Tests

2.3.2.1 The dry density

The density in hardened concrete was determined according to ASTM C642–97. The individual portion may be pieces of cylinders, cores, or beams of any desired shape or size, except that the volume of each portion shall not be less than 350 cm3 (or for normal weight concrete, approximately 800 g) , 100 mm cubes were used to determine the density. The density are calculated as follows: Bulk density, dry =[A/(C-D)]×ρ……(1) , where: A = mass of oven-dried sample , g ,B = mass of surface-dry sample in air after immersion, g ,C = mass of surface-dry sample in air after immersion and boiling, g 2.3.2.2 The ultrasonic pulse velocity test

The ultrasonic pulse velocity test was one of the non – destructive tests of the concrete. The ultrasonic pulses formed by the pulses which have high frequency over 20 Hz. The ultrasonic waves are made by the action of natural vibration for the crystal of materials .Concrete cubes of 100 mm were used, the PUNDT (the equipment that used to measure the UPV) setup in the laboratory with 54 kHz transducers and a calibration reference bar. Operation was relatively straight forward but it requires great care if reliable results were to be obtained . One essential was good acoustical coupling between the concrete surface and the face of the transducer and this was provided by a medium such as petroleum jelly , liquid soap or grease. This research used the direct transmission to the 100 × 100 × 100 concrete cubes. Recommendations for the used method were given in ASTM C597 –2003 .

V = L / T…(2) Where V = UPV, km/sec , L = Path length, mm and T = transit time, sec.

3 RESULTS AND DISCUSSION

3.1 The fresh test results :

All mixes showed a slump flow between 685 and 800 mm , T500 value ranges between 2.2 and 3.95 seconds , Blocking Ratio value ranges between 0.97 and 0.85, Filling Height value ranges between 3 and 20 and V-Funnel value ranges between 6.2 and 10.1 , while good resistance to segregation in the segregation test was observed. This results shows that it is possible to produce SCC by using polypropylene fibers and mineral admixtures .

3.2 Hardened concrete properties

3.2.1 The dry density

The results of bulk dry density on various types of concrete specimens are shown in Table (4) and Figures (1) through (3). Results indicated that all concrete specimens exhibited continuous increase in the density values with time of curing. This is mainly linked with the fact that with the progress of hydration, a continuous pore filling process is associated and the dry density increases with time, The relatively faster density development for mixes particularly at early ages was

believed to be mainly due to the inclusion of a superplasticizer, therefore, the interface zone becomes stronger, more homogeneous and dense. The bulk dry density results for SCC mixes without mineral admixture are considerably lower than ,SCC mixes with SF and SCC mixes with HRM .For example, the increases in bulk dry density for mixes (MSCCS) and (MSCCM) after 180 days compared with (SCC) mixes are (0.89%) and (1.09%) respectively. This demeanor was mainly related to the Pozzolanic reaction of SF and HRM with calcium hydroxide, forming calcium silicate and alumina silicate hydrates released from cement hydration and filling voids among cement or other powder material particles. This formulation provides increased density, resulting in reduced porosity and permeability. In addition, the dry density values of SCC mixes with HRM were higher compared to dry density values of SCC mixes with SF, as we observed from Table(4) and Figures(1). for example, the increases in bulk dry density for mixes (MSCCM) after 7, 28, 90 and 180 days were (0.21, 0.20, 0.6 and 0.2 )% respectively compared with (MSCCS) mixes. this is because of the higher Pozzolanic activity index of HRM compared to SF as mentioned in table (4) .On the other hand, the addition of PP fibers to the SCC mixes have negative effect on the dry density values. This behavior was obviously observed from Fig.1 and Fig.2, which shows SCC mixes with PP fibers have lower unit weight compared to SCC mixes without PP fibers. This behavior were ascribed to the low specific gravity of PP fibers and the formation of air voids which be associated with the addition of PP fibers. a higher fiber content also reduces the unit weight of concrete. When Fig.3 are considered, the dry density of f SCC mixes decreases with the increase of PP fiber length and consequently the unit weight goes down.

Table (4) the results of Bulk density and Ultrasonic Pulse Velocity measurements for all SCC mixes .

Mix

Mixture code

Bulk density kg/m3 at ages

of

Ultrasonic Pulse Velocity

(km/s) at ages of

7

days

28

days

90

days

180

days

7

days

28

days

90

days

180

days

1 MSCC 2309 2365 2421 2481 4.66 5.29 5.57 5.83

2 MSCCS 2331 2387 2443 2503 4.71 5.38 5.60 5.88

3 MSCCM 2336 2392 2458 2508 4.52 5.40 5.63 5.90

4 MSCC0.1PP6 2291 2355 2418 2475 4.61 5.26 5.56 5.81

5 MSCCS0.1PP6 2310 2381 2437 2497 4.65 5.36 5.58 5.86

6 MSCCM0.1PP6 2302 2386 2452 2505 4.43 5.38 5.61 5.89

7 MSCC0.1PP12 2280 2346 2403 2467 4.58 5.23 5.51 5.78

8 MSCCS0.1PP12 2299 2368 2425 2483 4.62 5.32 5.54 5.81

9 MSCCM0.1PP12 2291 2374 2440 2488 4.40 5.34 5.57 5.83

10 MSCC0.5PP6 2272 2352 2409 2469 4.56 5.25 5.53 5.79

11 MSCCS0.5PP6 2296 2375 2431 2492 4.61 5.34 5.56 5.84

12 MSCCM0.5PP6 2272 2380 2443 2496 4.35 5.36 5.58 5.86

13 MSCC0.5PP12 2261

14 MSCCS0.5PP12 2285

15 MSCCM0.5PP12 2253

Fig 1 :Effect of different curing period on bulk dry density

Fig 2 :Effect of %PP fiber volume on bulk dry density for SCC

Fig 3 :Effect of PP fiber length on bulk dry density of different curing period for SCC Mixes.

Mix 1 Mix 2 Mix 3 Mix

2100

2200

2300

2400

2500

2600

7 28 90 180

curing age (days)

Bulk

den

sity

2200

2250

2300

2350

2400

2450

2500

2550

0 0.1

Bulk

dry

den

sity

(Kg/

m3 )

2200

2250

2300

2350

2400

2450

2500

2550

0 2

Bulk

dry

den

sity

(Kg/

m3 )

2261 2333 2381 2464 4.53 5.19 5.44 5.77

2285 2353 2404 2483 4.58 5.27 5.47 5.81

2253 2361 2426 2485 4.30 5.30 5.52 5.82

Fig 1 :Effect of different curing period on bulk dry density for SCC Mixes.

Fig 2 :Effect of %PP fiber volume on bulk dry density for SCC Mixes with different curing period .

Fig 3 :Effect of PP fiber length on bulk dry density of different curing period for SCC Mixes.

Mix 4 Mix 5 Mix 6 Mix 7 Mix 8 Mix 9 Mix 10 Mix 11 Mix 12 Mix 13

Type of mix

0.2 0.3 0.4 0.5% fiber volume

4 6 8 10 12Fiber length (mm)

5.77

5.81

5.82

.

with different curing period .

.

13 Mix14 Mix 15

0.6

SCC 7 daysSCC 28 daysSCC 90 days

14

SCC 7daysSCC 28 daysSCC 90 daysSCC 180 days

3.2.2 The ultrasonic pulse velocity test results

Tables (4) and Figure (4) shows the results of Ultrasonic Pulse Velocity measurements for all mixes at ages of 7, 28, 90 and 185.82km/s . By using the proposed classification techniques which were proposed by (Jones & Gatfield),all produced concretes in this research are excellent quality .Test results show that the velocity of the ultrasonic waves for all specimens increases slightly with the increase in age of tested specimens up to 180 days. This increase is because of the progdecreases the void space within the concrete mass. The increase in the gel/space ratio causes a rise in wave speed, since the velocity of ultrasonic through materials is larger than that if it transfers through space. Hence, the incincreases the UPV. Table (4) and Figures higher as compared with MSCC concrete mixes. For example, for (MSCCS) specimens are (4.71, 5.38 , 5.6 and 5.88)( km/s) while 5.29, 5.57 and 5.83) (km/s) respectively . This improvement in reaction of silica fumes that leads togaps of the transition zone between the aggregates and cement paste and make it more dense which make the microstructure closer to cement paste than the microstructure of aggregates and cement paste .The Self compacting mixes that contain HRM have a significant effect on the results of UPV and this is attributed to the significant Pozzolanic activities of HRM that leads to densification of transition zone and thus leads to higher Velocity for these180 days of curing the percentage increases in compared to (MSCC) respectively, This is obvious from Figures (4).It is found that after 28, 90 and 180 days for (MSCCM) higher as compthe same Period .For example, UPV5.9)( km/s) while UPV for (MSCCS) are (5.38 , 5.6 and 5.88) (km/s) respectively, this is because of the significant Pozzolanic activities of HRM compared to silica fume which leads to more rehydration products for(MSCCM) than (MSCCS) which fill up and close the gaps of the transition zone between the aggregates and cement paste and make it more dense , this Enhanced the internal construction of MSCCM and made the size and content of voids and porosity less, which leads to an improvement in UPV

Fig 4 :Effect of different curing period on Ultrasonic Pulse Velocity

3.2.2.1 Effect of polypropylene fibers

Mix 1 Mix 2 Mix 3 Mix

47 28 90 180

curing age (days)

Ultr

ason

ic

plus

ve

loci

ty

The ultrasonic pulse velocity test results

the results of Ultrasonic Pulse Velocity measurements for all mixes at ages of 7, 28, 90 and 180 days. the UPV for all mixes ranged between 4.6

By using the proposed classification techniques which were proposed by (Jones & ll produced concretes in this research are excellent quality .Test results show that the

velocity of the ultrasonic waves for all specimens increases slightly with the increase in age of tested specimens up to 180 days. This increase is because of the progress of hydration which decreases the void space within the concrete mass. The increase in the gel/space ratio causes a rise in wave speed, since the velocity of ultrasonic through materials is larger than that if it transfers through space. Hence, the increase in the concrete mass within the same volume

(4) and Figures (4) illustrated that MSCCS mixes give higher as compared with MSCC concrete mixes. For example, UPV after 7, 28, 90 and 180 days for (MSCCS) specimens are (4.71, 5.38 , 5.6 and 5.88)( km/s) while UPV for (MSCC) are (4.66, 5.29, 5.57 and 5.83) (km/s) respectively . This improvement in UPV attributed to the Pozzolanic reaction of silica fumes that leads to increase rehydration products, which fill up and close the gaps of the transition zone between the aggregates and cement paste and make it more dense which make the microstructure closer to cement paste than the microstructure of aggregates and

te .The Self compacting mixes that contain HRM have a significant effect on the and this is attributed to the significant Pozzolanic activities of HRM that leads to

densification of transition zone and thus leads to higher Velocity for these mixes. At 28, 90 and 180 days of curing the percentage increases in UPV of MSCCM are (2.08 , 1.08 and 1.2)% compared to (MSCC) respectively, This is obvious from Figures (4).It is found that after 28, 90 and 180 days for (MSCCM) higher as compared with UPV values for (MSCCS) for

UPV after 28, 90 and 180 days for MSCCM are (5.4, 5.63 and for (MSCCS) are (5.38 , 5.6 and 5.88) (km/s) respectively, this is because

tivities of HRM compared to silica fume which leads to more rehydration products for(MSCCM) than (MSCCS) which fill up and close the gaps of the transition zone between the aggregates and cement paste and make it more dense , this Enhanced

struction of MSCCM and made the size and content of voids and porosity less, UPV.

Fig 4 :Effect of different curing period on Ultrasonic Pulse Velocity for SCC Mixes.

Effect of polypropylene fibers

Mix 4 Mix 5 Mix 6 Mix 7 Mix 8 Mix 9 Mix 10 Mix 11 Mix 12 Mix 13

Type of mix

the results of Ultrasonic Pulse Velocity measurements for all 4.66km/s and

By using the proposed classification techniques which were proposed by (Jones & ll produced concretes in this research are excellent quality .Test results show that the

velocity of the ultrasonic waves for all specimens increases slightly with the increase in age of ress of hydration which

decreases the void space within the concrete mass. The increase in the gel/space ratio causes a rise in wave speed, since the velocity of ultrasonic through materials is larger than that if it

rease in the concrete mass within the same volume ) illustrated that MSCCS mixes give UPV values

after 7, 28, 90 and 180 days for (MSCC) are (4.66,

attributed to the Pozzolanic increase rehydration products, which fill up and close the

gaps of the transition zone between the aggregates and cement paste and make it more dense which make the microstructure closer to cement paste than the microstructure of aggregates and

te .The Self compacting mixes that contain HRM have a significant effect on the and this is attributed to the significant Pozzolanic activities of HRM that leads to

mixes. At 28, 90 and of MSCCM are (2.08 , 1.08 and 1.2)%

compared to (MSCC) respectively, This is obvious from Figures (4).It is found that UPV values values for (MSCCS) for

after 28, 90 and 180 days for MSCCM are (5.4, 5.63 and for (MSCCS) are (5.38 , 5.6 and 5.88) (km/s) respectively, this is because

tivities of HRM compared to silica fume which leads to more rehydration products for(MSCCM) than (MSCCS) which fill up and close the gaps of the transition zone between the aggregates and cement paste and make it more dense , this Enhanced

struction of MSCCM and made the size and content of voids and porosity less,

Mix14 Mix 15

It is found that the addition of polypropylene fibers reduces the workability of SCC; hence, initiates the development of voids. The speed of UPV wave propagation is dependent on the material’s density and elastic property. The Ultrasonic pulse wave travels faster through solid media than through liquid and gas. In addition, the Ultrasonic pulse wave is highly sensitive for changes in the medium causes by The addition of high percentage of polypropylene fibers .Tables (4) and Figure (5) shows the effect of PP fiber volume fraction on UPV at different curing period for SCC concretes . For example, the percentage of decrease in UPV of MSCC0.1PP6 (addition of 0.1% of 6 mm polypropylene fiber in concrete mix MSCC) after 7, 28, 90 and 180 days of curing are (1.07, 0.6, 0.18 and 0.3)% compared to (MSCC) respectively, While the percentage of decrease becomes higher in UPV of MSCC0.5PP6 (addition of 0.5% of 6 mm polypropylene fiber in concrete mix MSCC) after 7, 28, 90 and 180 days of curing (2.15 ,0.76 ,0.72 and 0.7)% compared to (MSCC) respectively, This was obvious from Figure (5).Ultrasonic Pulse Velocity drops due to lower of density of the Transmission media which is caused by the presence of high air voids caused by adding fiber to the concrete mix and in general, the compressional wave tend to go as a straight path through the Transmission media as much as possible in the absence of obstruction. But when the carrier material contains some of the non-homogeneous materials the wave path and the time it takes the wave to move through the materials will be longer. The same effect was observed due to the effect of increasing the length of polypropylene fiber from 6mm to 12mm ,this was obvious from Figure (6).For example, the percentage of decrease in UPV of MSCC0.5PP6 (addition of 0.5% of 6 mm polypropylene fiber in concrete mix MSCC) after 7, 28, 90 and 180 days of curing are (2.15 ,0.76 ,0.72 and 0.67)% compared to (MSCC) respectively, While this reduction is increase in UPV of MSCC0.5PP12 (addition of 0.5% of 12 mm polypropylene fiber in concrete mix MSCC) after 7, 28, 90 and 180 days of curing and become (2.79 ,1.89 , 2.34 and 1.03)% compared to (MSCC) respectively. It was found from Figure (7) that, A linear correlation between UPV and bulk density represented by the equation y = 115.9x + 1809 (R2= 0.799), where y is the Ultrasonic pulse velocity and x the bulk dry density. This is exactly coincident with the results of Panzera et al 2008 .

.

Fig 5 :Effect of % PP fiber volume on UPV for SCC Mixes with different curing period .

4.24.44.64.8

55.25.45.65.8

6

0 0.1 0.2 0.3 0.4 0.5 0.6

Ultr

ason

ic p

lus

velo

city

(K

m/s

)

% fiber volume

SCC 7 daysSCC 28 daysSCC 90 daysSCC 180 days

.

Fig 6 :Effect of polypropylene fiber length on UPV of different curing period for SCC Mixes.

.

Fig 7 :Relationship between UPV and density for all curing period and different SCC mixes.

3.2.3 Conclusions The following conclusions can be drawn based on the results of this work.

1.The bulk dry density of SCC is less than that of SCC with silica fume or Metackoline at the same ages. The percentage decrease at age 28 days was (0.93%) and (1.14%) for SCCSF and SCCM respectively .On the other hand the bulk dry density of SCCSF is less than that of SCCM , with decrease at age 28 days was (0.21%) for SCCS.

2.The incorporation of polypropylene fibers decreases the bulk dry density of all SCC mixtures compared control mixes (0% fiber). The percentage decrease at age 28 days were between (0.42% to 1.35%) , (0.25% to 1.42%) and (0.25% to 1.30%) for SCC , SCCS and SCCM respectively .

3.The UPV of SCC mixtures was increased with the curing period of the specimens. This increase for SCC is about (13.51, 5.29, 4.66) % at age from (7 to 180) respectively.

4.The addition of mineral admixture increase UPV values of SCC mixtures.This increase for SCCS and SCCM were about (1.7,0.53, 0.86)% and (2.08,1.08,1.2)% compared to SCC at age from (28 to 180) respectively.

4.24.44.64.8

55.25.45.65.8

6

0 2 4 6 8 10 12 14

Ultr

ason

ic P

luse

Vel

ovity

(K

m/s

)

Fiber length (mm)

SCC 7daysSCC 28 daysSCC 90 daysSCC 180 days

y = 115.9x + 1809.R² = 0.799

2300

2350

2400

2450

2500

2550

4.2 4.7 5.2 5.7 6.2

Bulk

dry

den

sity

(Kg/

m3 )

Ultrasonic plus velocity (Km/s)

SCC

5.All adding 10% of Metakaoline leads to increases in the UPV in SCC mixes more than the addition of the same amount of silica fume. The percentage increase for SCCM compared to SCCS were between(0.34% to 0.53%) at age( 28,90 and 180) days respectively .

6.The presence of short and randomly distributed polypropylene fibers affects the UPV measurement negatively. Adding 6 mm of 0.1% PP fibers volume, the percentage decrease of SCC mixtures were between (0.17% to 2.65%) at age (7,28,90 and 180) days respectively.

7.Further addition of PP fibers (0.5%) did not improve UPV values .the percentage decrease of SCC mixtures were between (0.86% to 4.67%) at age (7,28,90 and 180) days respectively.

8.Increasing fiber length from 6mm to12mm led to more decrease in UPV values.The percentage decrease of SCC mixtures due to increasing fiber length were between(0.67% to 4.86%)at all age. 3.2.4 References Pons, G, M, Mouret, M, Alcantara, and J, L, Granju , "Mechanical behavior of self compacting concrete

with hybrid fiber reinforcement" Materials and structure Journal 2007 No, 40, pp,201-210. Persson, B, "on the internal frost resistance of self compacting concrete with and without polypropylene

fibers" Materials and structures Journal, 2006, No, 39, pp, 707-716. Liu, G, Ye, G, De, Schutter, Y, Yuan, and L, Taerwe," on the Mechanism of polypropylene fibers in

preventing fire spalling in self compacting and high performance cement paste" cement and concrete Research Journal, November 2007, Available online at www,Sciencedirect,com .

Bauml, M, F and WittMann, F, H, "Improved Durability of self compacting concrete by addition of fibers" proceeding of the second International symposium on self compacting concrete, Edited by Kazumasa Ozawa and Masahiro Ouchi in 23-25 October 2001, Tokyo, Japan, pp, 527-535.

Panzera T. H., Rubio J. C., Bowen C. R., Vasconcelos W. L., Strecker K. (2008). Correlation between structure and pulse velocity of cementitious composites. Advances in Cement Research, Vol. 20, No. 3, July, pp. 101–108.

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